An electric motor to be mounted on a compressor of a refrigerating air-conditioning apparatus is required to satisfy energy saving and low noise and to ensure the use in a high-temperature atmosphere at about 150° C. In general, a Nd—Fe—B based rare-earth magnet has a high residual flux density and hence is suitable for miniaturization and an increase inefficiency of the electric motor. However, as temperature increases, the magnetic coercive force of the Nd—Fe—B based rare-earth magnet decreases. Therefore, there is a problem in that, in the comparison at the same current, electric motors used in a higher temperature atmosphere are more liable to be demagnetized. Therefore, heavy rare-earth elements such as dysprosium (Dy) and terbium (Tb) are added to a rare-earth magnet to be used in a high-temperature atmosphere so as to increase the magnetic coercive force of the rare-earth magnet, thereby preventing the rare-earth magnet from being demagnetized. However, in recent years, the rarity value of the heavy rare-earth elements has increased, and hence the risks of the difficulty in procurement and the rise in prices are increasing. Reflecting such a situation, there is a demand for an electric motor satisfying high efficiency and low noise, in which even a rare-earth magnet having a low magnetic coercive force is less liable to be demagnetized.
In this respect, in Patent Literature 1, there is disclosed a rotor of a permanent magnet electric motor in which a hole for preventing a flux short circuit is formed in a rotor core so as to be brought close to an outer periphery of the rotor core, and the hole for preventing a flux short circuit is formed so as to be brought into contact with a hole for embedding a permanent magnet and an end portion of a permanent magnet to be embedded in the permanent magnet embedding hole. In this rotor, it is expected that the flux short circuit preventing hole prevents a short circuit of a flux in the end portion of the permanent magnet, and the flux in the end portion of the permanent magnet extends to a stator so as to effectively serve to generate a torque, and thus a permanent magnet electric motor having high efficiency and a low cogging torque and having less vibration and noise is obtained.
Further, in Patent Literature 2, there is disclosed a rotor of a permanent magnet electric motor, which has a plurality of slits arranged at a distance along a permanent magnetic insertion hole, and an outer thin portion formed between an outer end of a radial direction of the slits and an outer periphery of a rotor core, the width in the radial direction of the outer thin portion being gradually enlarged from a magnetic pole center to an interpolar portion. In this rotor, it can be expected that a harmonic wave component of a flux density waveform be decreased so as to reduce a harmonic wave of an inductive voltage and a cogging torque.